The present invention relates to a permanent magnetic type electric rotating machine having a permanent magnet for a field in a rotor, and more particularly to a permanent magnetic type electric rotating machine suitable for use in a compressor of an air conditioner, a refrigerator, or a freezer.
In permanent magnetic type electric rotating machines of this kind, various attempts have been made to reduce noise and vibration, that is, to reduce torque pulses. For example, as described in JP-U-3-106869 specification, centers of tips of stator teeth form a circle concentric with a rotor core, and both ends of the tips of the teeth are formed in a straight line, that is, placed apart from a rotor to thereby reduce torque pulses.
When a harmonic current passes through armature winding of the permanent magnetic type electric rotating machine, a harmonic magnetic flux is generated to increase the torque pulses, so that reducing the harmonic current is important for reducing noise and vibration. A waveform of an armature current depends on a waveform of a voltage applied on the armature winding and a waveform of a back electromotive force (induced electromotive force), and thus the waveform of the induced electromotive force may be brought close to a sine wave.
In the above described conventional technique, both ends of the tips of the teeth are placed apart from the rotor to smooth magnetic flux distribution in the machine (or to bring the waveform of the induced electromotive force close to the sine wave) and to thereby reduce the torque pulses. However, the farther from the rotor the both ends of the tips of the teeth are placed, the smaller sectional areas of slots become, thereby preventing insertion of the armature winding. Thus, there is a limitation in reducing the torque pulses by a tip shape of the teeth.
An object of the present invention is to provide a permanent magnetic type electric rotating machine sufficiently reducing torque pulses and causing low vibration and low noise.
In order to attain the above described object, the present invention proposes a permanent magnetic type electric rotating machine including: a stator having armature winding arranged in a plurality of slots formed in a stator core; and a rotor having permanent magnets held in a plurality of permanent magnetic insertion holes formed in a rotor core, wherein a peripheral surface of the rotor core is configured in such a manner that when an axis extending in a central direction of a magnetic pole of the rotor is d axis, and an axis extending in a direction between magnetic poles that is offset from the central direction of the magnetic pole by 90 electrical degrees is q axis, and a radial distance from a center of the rotor core to a periphery of the rotor is reduced gradually from the d axis to the q axis.
The present invention further proposes a permanent magnetic type electric rotating machine including: a stator having concentrated armature winding arranged to surround teeth in a plurality of slots formed in a stator core; and a rotor having permanent magnets held in a plurality of permanent magnetic insertion holes formed in a rotor core, wherein a peripheral surface of the rotor core is configured in such a manner that when an axis extending in a central direction of a magnetic pole of the rotor is d axis, and an axis extending in a direction between magnetic poles that is offset from the central direction of the magnetic pole by 90 electrical degrees is q axis, and a radial distance from a center of the rotor core to a periphery of the rotor is reduced gradually from the d axis to the q axis.
As described above, in order to reduce vibration and noise of the permanent magnetic type electric rotating machine, it is necessary to suppress harmonic magnetic fluxes generated by a harmonic component of an armature current and to thereby reduce torque pulses. The harmonic component of the armature current depends on a waveform of a voltage supplied to a terminal of the permanent magnetic type electric rotating machine and a waveform of an induced electromotive force, and thus it is important to bring the waveform of the induced electromotive force close to a sine wave.
The present invention allows the waveform of the induced electromotive force of the permanent magnetic type electric rotating machine to be brought close to the sine wave by a peripheral shape of the rotor core. Therefore, the harmonic component of the armature current are reduced to thereby significantly reduce the torque pulses, thus providing a permanent magnetic type electric rotating machine causing low vibration and low noise.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.